CHATHAM — Last summer as many as a dozen great white sharks were seen swimming in the waters off Chatham, feeding on seals that congregate in one of the largest gray seal colonies in New England.

So, it's no surprise the town has a comprehensive plan in place, using harbor patrol boats and beach patrols to spot sharks and get the word out.

Warnings were issued earlier this week after a 15-foot great white was spotted Sunday afternoon chasing seals south of Nauset Beach in Orleans.

Despite the great white sighting, experts say there is no evidence there are a lot of sharks in Cape waters.

Pilot George Breen was flying along the coast Sunday, in search of bluefin tuna for commercial fishermen, when he saw the great white shark pursuing the pod of seals. Breen made another flight Monday from Monomoy to Wellfleet and didn't report seeing any sharks.

Although he doesn't take the shark threat lightly, Cape Cod National Seashore Chief Ranger Bob Grant says the primary food source for great whites is on Monomoy. With the exception of a few hundred seals in the High Head area of North Truro, there is little reason for great whites to venture north.

"Our thought process is that (sharks) are in the Chatham/Orleans area," Grant said.

Seashore lifeguards on protected beaches, and a guard on an all-terrain-vehicle patrolling Marconi, Nauset Light and Coast Guard beaches, watch for fins in the water. They raise a blue flag to signal that sharks have been spotted, and they keep people out of the water until there has been no sighting of a fin or shark for at least an hour.

Grant said the town police dispatchers have park service radios, and they enjoy a close relationship with town departments and would be contacted if a spotter plane or boat saw a great white in their area.

If a shark is spotted in Chatham, or they get a warning from planes or vessels of one in local waters, the information is posted on the town web site and aired on local cable access Channel 18. Other town departments also are notified.

Even though it's a relatively short swim from Chatham to Wellfleet and Truro for these big sharks, officials at the Cape's northernmost beaches continue to rely primarily on lifeguards to keep an eye out for the great whites.

"The question we get is, 'Have you seen them up here?' And the answer is, 'Not recently. Not here,'" Wellfleet Beach Administrator Suzanne Grout Thomas said.

If a shark were spotted by a plane or boat near Wellfleet beaches, the police department would contact her, she said. Aside from that, her lifeguards watch the water as they always have, looking for fins, getting people out of the water when a shark passes by, and calling ahead to the next beach in its path.

State Division of Marine Fisheries spokeswoman Catherine Williams said her agency does not want to issue false reports on a great white sighting and that Greg Skomal, the DMF shark expert, analyzed the photographs Breen sent him before confirming the attack.

Smith received a call from Skomal mid-morning Monday and relayed the information to Orleans Harbor Master Dawson Farber, who called Parks and Beaches Superintendent Paul Fulcher.

Generally, an Orleans harbor master's boat would have been dispatched to cruise along Nauset Beach and look for the shark, but that was not done because the sighting happened the previous day. Fulcher was planning on speaking with Skomal about how the town might get information sooner.

But Smith thought the system had worked well.

At this point, there aren't enough sharks in the area to have spotter planes looking exclusively for great whites, but Smith said he has been talking almost daily with Breen, who was the pilot who helped Skomal find the five great whites he tagged last summer. He said he also speaks frequently with Skomal.

"I think the lines of communication with the (DMF) are pretty good," Smith said yesterday.